Many locomotives employ engines that combust fuels to generate mechanical and/or electrical power for propelling the locomotive and powering its various support and control systems. Such fuel-consuming engines exhaust a complex mixture of pollutants, including particulate matter, oxides of nitrogen, and other constituents. To satisfy increasingly stringent exhaust emission standards and to meet fuel efficiency goals, locomotive manufacturers have implemented various aftertreatment systems and control strategies. Typical aftertreatment systems incorporate one or more filters, catalysts, and/or other devices that utilize heat generated by the associated engine to reduce, convert, burn, or otherwise treat pollutants in the exhaust. Some control strategies include placing loads on the associated engine to heat the aftertreatment system.
Most aftertreatment devices must achieve a minimum temperature in order to sufficiently reduce pollutants (e.g., a light-off temperature, an activation temperature, a regeneration temperature, etc.), and achieving this minimum temperature can be difficult when the engine is not producing a sufficient amount of heat. Circumstances when the engine may not produce a sufficient amount of heat include, for example, after the engine has been restarted following a period of rest and when the engine is running at idle speeds. However, locomotive operators often run the engine at idle speeds for extended periods of time instead of shutting it down to avoid the possibility that it will be difficult to restart the engine and/or to avoid cutting power to various systems and devices that are powered by the engine during idle operations (e.g., cab heating/cooling, compressed air for brakes, electrical systems, etc.). During these periods when the load on the engine is low, the engine may not produce enough heat for the aftertreatment system to effectively reduce emissions and may continue to consume fuel with the locomotive having zero speed, thereby lowering the average fuel efficiency of the locomotive.
One attempt to increase the temperature of an aftertreatment device is described in U.S. Pat. No. 6,422,001 (the '001 patent) that issued to Sherman et al. on Jul. 23, 2002. The '001 patent describes a method of regenerating a particulate filter of a hybrid electric vehicle. When the backpressure of the exhaust system exceeds a threshold, a controller increases the speed of the engine and applies other loads to the engine to increase the temperature of the particulate filter. The loads are applied to the engine by increasing the power output of a generator driven by the engine by connecting the generator to a power dissipating device such as a resistor. The controller controls the engine speed and load according to a map that correlates a filter regeneration temperature to an engine speed and torque output for achieving that temperature.
Although the system of the '001 patent may be somewhat effective at increasing the temperature of an after treatment device, it may not be optimal. In particular, the system of the '001 patent is directed to the periodic regeneration of a particulate filter and may not be applicable to increasing and maintaining the temperature of an aftertreatment system that includes other devices that should constantly be above their activation temperatures. The system of the '001 patent may also fail to consider the current temperature of the aftertreatment system in determining how much to increase the load on the engine, which may lead to wasteful heating of the aftertreatment system. Further, the system of the '001 patent may not account for the temperature needs of aftertreatment devices during idle conditions, which may lead to insufficient or wasteful heating of the exhaust system.
The system of the present disclosure solves one or more of the problems set forth above and/or other problems of the prior art.